How do I deal with my mother's financial debt and siblings who are financially exploiting her?

You're right that this is a mess. Since your mother has dementia, it may help to see if you can get her away from this family and into a nursing home. Her house could be sold to pay off her debt and what is left would pay nursing home costs until she qualified for Medicaid. She may feel protected in a controlled environment and she'd have peer interaction and socialization.
Other than that, there isn't much you can do unless you want to get an attorney to help straighten this out. Your mother is giving over the money of her own free will, so her dementia would need to be brought to light and then the attorney may be able to stop this exploitation. This could be a lengthy process, however. Also, this approach will likely end your relationship with your siblings. It's a tough choice. One consultation with an attorney, at least, may give you some ideas of how to move forward. Good luck,
Carol

I am in the same boat - only having to fight two brothers who are draining my poor Mom's account. They have turned against me and managed to turn the rest of our family against me as well. I am 1000 miles away from My Mom and brothers which makes it even more difficult. Any attorney is the only answer! Get it going now.

Yikes, sounds like a bad situation, but is there any silver lining to your siblings living with mom? Are they by caring people who will stay there with mom if she starts to need lots of help? If not, it might be best to start the process of having mom qualify to enter a nursing home. But if they are dependable in terms of caring for mom, there might be some positives in this situation. It sounds like your siblings have about reached the bottom of mom's bank account. At that point, you'll actually be able to stop worrying about your mom's finances if her monthly income is enough to provide for her necessities. She can just stop paying on her credit card debt (and shred the card!). Your mom probably has little need for a good credit rating at this point and, frankly, it will take a long time for them to come after her over it (ignore the obnoxious calls and collection notices). With your brother as co-owner, the house becomes his problem. He's at an age where he should be protecting his credit rating by at least paying his half of taxes and mortgage each month.

I'd focus on getting control on your mom's essentials. Open an account in both your names and have her monthly income deposited there. I know, easier said than done! But if that's where you focus your energies (instead of your anger at bro and sis for bilking mom), you can win. Explain that it's your contribution to caring for her. You can pay her important bills (not the credit cards!) and write her a monthly check for her discretionary spending (try not to think about whether or not she's handing it all over to your siblings).

This is a tough situation, channel your energy into actions that can make it better (and, to preserve your sanity, have regular, long, anger-venting sessions with a good friend !).

I agree. fly to mom. set up a joint account and if she is competent have her transfer her current monies to the new account that you can manage. Just as important, can you be her POA. You can call attornies in advance but do not mention the dementia yet if she is still competent. A good elder attorney can help you better than us.